The invention relates to a method and a device for producing a dispersed mixture; and
Dispersing refers to the dispersal and smallest possible distribution of one material in another one. The finished mixture is then referred to as dispersion. A dispersion means that one or several dispersed phases, the inner phases, are present in a continuous phase, the outer phase. If the dispersed phase is completely soluble in the continuous phase, then the dispersion immediately changes to a homogeneous mixture. Typical examples of dispersions produced through dispersal in the field of chemical process engineering include:
Liquid--liquid systems: PA1 Gas-liquid systems: PA1 Liquid-solid material systems:
emulsions (dispersed phase: liquid, continuous phase: liquid); examples: oil-in-water emulsions, water-in-oil emulsions PA2 aerated liquids or melts (dispersed phase: gas, continuous phase: liquid), e.g. foam products PA2 mist (dispersed phase: liquid; continuous phase: gas) PA2 suspensions (dispersed phase: solid material; continuous phase: liquid) for which the solid material phase is realized during the dispersion process, for example, through precipitating out of a supersaturated, dissolved material.
Dispersal refers to the purely physical action of dispersing, as is the case for producing emulsions. The dispersing action is used, for example, as introductory, primary dispersing step or as re-dispersing step that follows a primary dispersal when realizing chemical reactions in two-phase or multiphase reaction systems.
When realizing chemical reactions, the ratio of material transport speed to kinetics determines to what degree the reaction sequence can be accelerated through intensifying the dispersion operation, meaning by increasing the interfaces between the phases involved in the reaction. Thus, for very fast chemical reactions, the material transport between the phases involved in the reaction as a rule is critical for the chemical conversion speed and thus for the reactor output that can be achieved. Accordingly, an essential object during the dispersing operation is to generate the highest possible interface per reaction volume, meaning the smallest possible particles to be dispersed (e.g. liquid drops, gas bubbles) and to minimize the energy expenditure required for this.
It is the object of technical dispersion processes to disperse and finely divide one or several components equally and reproducibly in a continuous phase. The various goals to be achieved in this case are, among other things, the reproducible production of dispersions with defined particle sizes for the dispersed phase, the smallest possible particles with correspondingly large volume-specific interface between dispersed and continuous phase, as well as narrow particle size distributions. The dispersion device used for the dispersing must be configured and designed in such a way that it can handle the dispersing task with minimum energy expenditure, meaning with high efficiency.
Many different dispersion devices are presently used for the dispersion process. In principle, a distinction must be made between dynamic dispersion devices and static dispersion devices.
With dynamic dispersion devices, the dispersed phase and the continuous phase are generally put into motion, wherein energy is introduced by way of the turbulent flow energy of the phases in motion. For static dispersion devices, only the dispersed phase is generally put into motion.
Dynamic dispersion devices for liquid--liquid systems include, for example, nozzles, nozzles combined with subsequently installed stream-dispersing means, stirrers, as well as rotor-stator systems; for gas-liquid systems, for example, they include injectors or ejectors, Venturi nozzles and stirrers, and for liquid-solid material systems, for example, they include precipitating nozzles and stirrers.
Static dispersion devices for liquid--liquid, gas-liquid, as well as solid material-liquid systems include, e.g. push-in pipes, sieve plates, perforated plates that are made of metal, rubber or plastic, optionally also with pulsating plate, pipe distribution rings as well as sintered plates made of glass or metal. Sintered plates are preferably used for gas-liquid systems.
The disadvantage when using known dynamic dispersion devices is that the distribution of the dispersed phase occurs in a spatially expanded, turbulent shear field, wherein the unequal distribution of the local energy dissipation rates leads to broader particle size distributions for the dispersed phase. In order to produce dispersions with low average particle dimensions for the dispersed phase and correspondingly large, volume-specific interfaces, a comparably high energy expenditure is required.
In contrast to dynamically operated devices, the static dispersion devices available at present generally have a more favorable energy ratio, meaning the ratio of generated volume-specific interface to energy expenditure provided is higher. The absolutely achievable, volume-specific interface that can be achieved with static devices, however, is generally small.
The German Patent 44 16 343 A1 discloses a static micro-mixer, which consists of a stack of foils. Parallel systems of slanted grooves are worked respectively into one side of the foil. The foils are stacked in such a way that the slanted grooves of each second foil extend in a mirror-image arrangement to the grooves of the two neighboring foils. Together with the smooth side of a neighboring foil, the grooves then form closed channels. The micro-mixer can be used to mix fluids, in such a way that the slanted channels are alternately admitted with respectively one fluid. When the fluids exit from the micro-mixer, minute fluid streams are formed, which intermingle completely. With the micro-mixer, the mixing operation therefore occurs outside of the device.
The subject matter of the German Patent 44 33 439 A1 is a method for realizing a chemical reaction by means of the device, described in the above-mentioned German Patent 44 16343 A1.
A micro-reactor is described in the German Patent 39 26 466 A1 for which the mixing of fluids is to take place inside the micro-reactor. Two reaction partners A and B are separated into partial flows by a laterally extending groove that is provided in an intermediate foil and forms a mixing space. Two fluid flows are conducted in parallel micro-channels, extending immediately below or immediately above the intermediate foil. These fluid flows must be mixed in the laterally extending groove of the intermediate foil. The channels below the intermediate foil are arranged perpendicular to the channels above the intermediate foil. With respect to design, this results in a foil triplet, comprising a foil for A, an intermediate foil with the laterally extending groove, and a foil for B. A plurality of such triplets can be stacked one above the other.
With the known micro reactor, the still unmixed liquids flow through channels of different lengths until they reach the laterally extending grooves. This results in at least one incomplete mixing within the micro reactor. In addition, a share of the two material flows should respectively pass by the laterally extending groove and be conducted further in the channels for the respectively other material flow. This would lead to a high pressure loss in the respective shares. For that reason, the known micro reactor cannot be used without modifying the design as shown.
The WO-A-9630113 discloses a device for mixing small amounts of liquid, wherein a liquid to be mixed thoroughly enters an inlet channel, is divided there into at least two branching-off micro channels that are positioned in one plane and is subsequently combined again with the aid of a confluence element that is rotated by 90.degree. relative to the plane. From this confluence element, the liquid is then conducted into an additional micro channel in the plane. The additional micro channel can form the inlet channel for another such device. The device does not comprise separate inlet channels for the liquid components to be mixed.
It is the object of the invention to provide a method and a device for producing a dispersed mixture from at least two phases, wherein the mixture is produced inside of the device. A less severe pressure drop must occur during the dispersion of the phases.